Telephone system



March 19, 1929.

C. GILL! NGS TELEPHONE SYSTEM Original Filed June 30, 1924 4 8 Sheets-Sheet 1 Ihlllllll E] Illllll ll March 19, 1929. glLLlNGS 1,705,832

TELEPHONE SYSTEM 1 Filed June 50, 1924 8 Sheets-Sheet 2 Origina Ehaples 'Elllmgs TELEPHONE SYSTEM Original Filed June 30, 1924 8 Sheet -sh et 3 I 4 L T 4; U

-Im.rsn Elf-- Eharlas 512M1 5 March 19, 1929. I 3, GILLINGSY 7 1,705,832

TELEPHONE SYSTEM Original Filed June so, 1924 a sheets-sheet 4 it A? ii-F 505 Imren 01 Eharles Efllmgs v WWW 311g;

March 19, 1929. c. GILLINGS I TEIJEPHONE SYSTEM Original Filed we so, 1924 a Sheets-Sheet 5 March 19, 1929.

c. GILLlNGS 1,705,832

TELEPHONE SYSTEM 8 Sheets-Sheet 6 Original Filed June 30, 1924 Eharlss, 312217.195

March 19, 1929. c, NGs 1,705,832

" TELEPHONE SYSTEM Original Filed J1me 1924 8 Sheets-Sheet 7 -In-7./en2ar' Charles Ezllmgs March 19, 1929. c, lLLmss 1,705,832

TELEPHONE SYSTEM Original Filed June 30, 1924 8 Sheets-Sheet 8 48 J43 J50 In up Bhar'les 1311111195 Patented Mar. 19, 1929. I

- N ED T AT N QFFIQE- ci-IenLEs GILLI NGS, or LIVERPOOL, ENGLAND, ASSIGNGRLBY MESNE ASSIGNMENTS,

T0 AUTOMATIC ELECTRIC nc; or onroneo, fILLIivo s, A CORPORATION or DELA- WARE. I I 1 Application filed June 30, 1924, Serial The present invention concerns improve-'- ments in or relating to telephone systems and more particularly to those systems in whlch f calls are set up from a manual subscriber over numerical switches controlled by an ope 'ator. In the Patent No. 1,651,401 to Mercer and T ench, an arrangement is described in which .4 v u I 1 It has been found, more particularly in r of example. only,

large networks, that it is desirable. to have means for translating the; whole or a portion of a number set up by the operator so that impulsesmay be sent out which do not correspond with the number set up;

The present inventionprovides an impulse sender adapted to bring about this result in anarrangement on the general l nes dlsclosed in the application above referred to.

of keys adapted to be operated in accordance with the exchange and the number ofawanted partv is arranged to control the transmission of impulsesthrough the intermediaryoi a translating device to route the call to the through the intermediary of a translating device the transmission of series of impulses which may differ n number and value from the number set up on the: "digit keys to route the call to the desired exchange.

A further feature of the invention is the use of an impulse sender infwhich certain sets of a plurality of sets of storage relays correspending in number to the number of digits in the designation of a subscriber, are adapted to control the transmission of impulses through the intermediary of a translating device, i

February 14, 1929."

- jack J TELEPHONE sYs'rEM.

No. 723,124, and in Great Britain Ju1 '12, 1923. Renewed i Still another featureof the invention is the provision ofan impulse sender controlled by a set ofkeys under the controlof an operator in which predetermined series of impulses having no numerical relationship to the number set up, are a'dapted to be trans mitted automatically to route the call to an operators position when the impulse sender is set for a number which doesinotcorrespond" to a subscribers number.

These andother features not specifically mentioned at this point'will be more fully" understood from the following description of a preterred' form ofthe invention,though 1t Wlll be understood that this is given by way tions could be'ma'de inthe circuit details with out exceeding'the scopeof the'invention.

Referringnow to the accompanying draw tings, 1 shows schematically the'general layout of-the'system while 'Figs Q 'to'8 show by means ofdetailed circuit diagrams' the actual apparatus used by an operator inthe mechanical tandem exchange in setting-up According to one f at f h in i a-connect1on from a subscriber of a manual an impulse sender is provided in which a set exchange'to an automatic subscriber in av third exchange. r

Consideringfirst Fig. 1,'the operations involved -in.'setting up "a call will be traced through. When the manual sub-- scriber'A removes his, receiver, he attracts the attention of the operator at his exchange in the usual manner and she thereupon inserts the answering plug P of the cord 0 into his -Upon learning his requirements, she will: communicate with the operator at the mechanical, tandem exchange over an order wire (not shown) and inform her of the number of the wanted party. She will then be assigned a free junction line, for instance the line L and will thereupon insert the plug P into the'jack J The B operator atthe tandem exchange at the same time as she notifies; the Aoperator of the'junction line to be used, will press the assignment key associated with this line, whereupon the sender selector SS associated with the o utlet with which the wipers of the outlet finder OF are then in engagement will be start-ed up and commence huntand that variousmddificaing to find an idle set of impulse sending equipment. When this is found it will be associated with the key set K, and the B operator will be notified by the lighting of a lamp. She will then setup the number on the key set and in accordance with the first digit the first storage relay group SR will be influenced over the outlet finder OF in the position shown, back contact and armature T sender selector SS armature and its back contact, transfer switch TS in first position to first storage relay group SR Upon the release of each key the transfer switch will be moved on one step so that each digit of the required number will be stored on the appropriate set of storage relays SR SR SH, SH SR When theB operator presses her start key (assuming that the plug 1 has already been inserted in the jack J the armatures T and WW will be operated and the code switch CS will be started up and will proceed to hunt until it finds terminals which have been marked by the operation of the storage relay groups SR SR and SR, whereupon the shunt field relay SF is operated and stops the switch CS.

The first three contacts of the sender control switch SCS are then controlled over another set of Wipers of the switch CS so as to eiiect the sending of trains of impulses which will in general differ in value and possibly also in number from these corresponding to the number recmfded on the relays of the first three storage relay groups. The. circuit for the transmission of impulses extends from the impulse sender IS over front contact and armature VV sender selector SS armature T and its front contact to the connecting point C and thence over the line L to the selector E. Further impulses then operate selectors such as F and succeeding selectors and a connector. The sender control switch SGS is moved on one step after the termination 01" each series of impulses and after the first three series have been sent engages its fourth bank contact. Bank contacts 4, 5, (3 of the switch SCS are connected to the code relays CR which are only used in case it is desired to send more than three exchange digits. It, as will usually be the. case only three exchange digits are bein sent, the switch SSS will be moved quickly through positions 4., 5 and 6 to position 7, in which position the impulse sender is controlled by the storage relay group SR- to send the first numerical digit. The remaining nun'ierical digits are then sent in the usual manner under the control of storage relay groups SR SR and SR. In this case the transfer switch T S is not released when the transmission of impulses cominences but'remains in operated position throughout the sending of impulses, and is released with the remainder of the apparatus when this is finished. V

The, outlet finder OF is moved on one step each time the start key is'operated so that the operator may commence setting up another connection. as soon as she has finished with the previous one. v I

The selector E may have access to a selector F in common with a line coming from an automatic subscriber whose connections will be set up over the individual line switch {I with the aid of the director or register translator D. l/Vhen the connection has been fully set up the contact B is closed and the director cut out.

Referring now more particularly to Figs. 28 the operations involved in the sending oi? a call will be traced through in detail. The A operator in the originating manual exchange, after ascertaining the calling subscribers wishes ill communicate with the B operator at the mechanical tandem exchange over an order wire which is not shown. The B operator will thereupon assign to the A. operator an idle junction line, for instance, that, comprising conductors 302 and 303. At the she will press the corresponding assignment key 304' whereupon the assignment relay 305 is energized and operates its contacts 306, 307 308, 309 and 310. At armatures 306-309 inclusive, circuits are prepared for the trunk connecting relays 312, 313, 314 and-315. It will be assumed "for the purpose of description that the first outlet in the one which is to he used and consequently'the only arn'iatur-e which will perform any useful function in this case is armature 306 which prepares a cir connected by way of a chain of contacts such as armature 311 on all the assignment relays to lead 400 which extends to equipment ind1- vidual tothe position and common to'all the ment, normally closed spring 462 of the sender disconnect key, armature 434 and its back contact, relay 420 to battery. Relay 403 operates its armatures 452 and 453 thereby closing contacts for a purpos which will be fully described. hereafter. Relays 40S) and 410 at contacts 465 and 463 control a circuit for the driving magnet 467. As. however, re lay 409 is slightly slow to pull up. contact 466 will always be c tmncd before contact 455 closes and a circuit will in the normal course of operation never be completed for magnet 467, even should earth be connected to lead 439 which will not in general be the case. Relay 420 upon energizing at armature 432 completes a circuit for cut off relay 419 and driving magnet 445 in series which circuit may be traced as follows: earth, resting contact and armature 49.2 armature 456 and its resting contact. wiper 455 and the contact with which it is in engagement, armature 452 same time p cuit for relay 312. At armature 3.10, earth is nets-.45 in the-above circuit.

I leads 402. ant

5 contact, armature 432 and its working contact, winding of relay 419, internipter contact'446, driving magnet 445 to battery. connects the test wi per 474 of the sender selector by way of resting contact and armature 451 and armature 431 and its resting contact to the junction of relay 4.19 and driving mag- Consequently it there is an earth on the contact with which wiper 474 is in engagement, relay 419 will be short circuited, and the switch will commence to hunt in the usual manner until wiper 474 engages with a contact which is not earthed. When this occurs, relay 419 will energize in series with driving magnet 445,.which latter however, does not now receive enough cur rent to energize it. Belay 419 upon operating, at armature 430 completes a locking circuit for itself to the earth on back contactof armature 444, at armature 431 disconnects the and its working driving magnet445 and )lLtCGS earth on test I wiper 474 and armature 429 completes a circuit'ior relay 418. Relay 41S, upon operating, at armatures 424, 425 and 426 connects the wipers 450, 457 and 458 through to the wipers 470, 471, 472 respectively, wiper 459 having previously been connected through to wiper 47 iiat'armature 428 by the operation 04 relay 419. At armatures 475 and 427, battery and earth respectively are connected to 403 extending to the trunk circuit, the earth connection to lead 403 being over the normally closed spring 464 of the sender disconnect key. A branch circuit from this spring also extends to the sender guard lamp 476 which therefore lights and indicates that the corresponding outlet is in use. The connection of earth to test wiper 474, in addition to making the impulse sender busy to other sender selectors, has the eil ect of energizing relay 525. This. relay there upon operates at armature 526 opens a point in the circuit of release magnet 508 so that this will not operate when the oil-normal contat 509 close.'at armatlu'es 527 and 528 open, .ints in the circuit of release relay and atarmature 530 closes a chain li usyinn circuit the nature and code of operation oi which will. be fully described subsequently. I

The. eltect oi the connectionof battery and earth to the lQL is 402 and 403. is to complete an ene zine; circuit for the trunk'connectingrelay 312 which circ from the battery connection on lead '1 may be traced,

402 by- *ay'ol the normally closed contacts COH- trolled by armature 32.0,winding of relay 312 and armature 306 and its working contact to earth on lead 403. Relay 312 therefore operates-1, at its armatures 316 and 317 connects the outgoing trunk conductors 336 and 337 to the impulsingr leads 405 and 407, and at armature 313 completes a circuit cm the normal loatter Y connection on lead 406 b wa of restin l I I l y I 3 Relay 420 also at armature 433 point in the contact and armature 439 to the assi 'mnent lamp 322, armature 332 and its resting con- 320 opens its initial energizing circuit and" completes a locking circuit for itself by way or the normally closed spring 326 ofthe busy or cancel key and at armature 321 shunts armature 306 so that its own circuit'is not interrupted when relay 305 deenergizes upon the release of the assignment key 304. The operator keeps the assignment key pressed until the 1211113322 h 'hts whereuoon she knows a that the outlet jhnder and sender selector switches are. functioning correctly and that her key set is now connected to an idle set of impulse sending equipment. r

The apparatus isnow in readiness for reg.- i s teringthe wanted number as set up upon the key Suppose that the numerical equivalent ol' the wanted number is 3765432.

, hen the key 8 is pressed a circuit is completed fromearth, operated spring of digit key 8, lead 480, wiper 457 and the contact'with which it is in engagement, front contactxand I armature 425, back contact and armature 440, wiper 471, lead 501, armature back contact, wiper 539 of the transfer switch in 'firstposition, lead 556, lower relay 560, lead 563, back contact and armature 519, winding of relay 514 to battery. Be lays 514 and 560 energize in this circuitand theformer at armatur'e515 completes a circuit for relay 510, at armature 516 opens a point in the circuit of the stepping magnet 507, and at armatures 517 opens a point in cuit of relay 531 which is madeslightly slow to pull up. "Relay 510 upon operating, at armature 511reinoves earth from the eighth contact-in the bank of wiper 538, which opera.- tion serves no particular purpose at the present time at armature 512 jn'eparesa circuit "for, the steppingmagnet 507fand at armature 513 opens another'point in the circuit of re lay 531. Relay 560 upon operating, at arma lure 564 completes a locking circuit for itself through its upper winding to lead 552and thence over back contact and armature F and lead 504 to earth at armature 427. Relay 500 also operates its arnniturcs 568 and 570 but this is without any immediate A similar circuit is also completed from the other operated spring of digit key Sever lead 481, wiper 458 and the cont-act with which it is in engagement,front contact and armature- 426, back contact and armature 441, wiper 472, lead 502', armature535 audits back contact, wiper 540 of thetranst'er switch in first position, lead557; lower winding relay 561 to lead 553 and thence to battery throughthe winding of relay 514 as before. The effect of the current lay514 is the same as previously described,

534 and its.

winding or flowing through rewhile relay 561 operates and locks itseli up 503 for the relays 57 5 and 576 in the third to lead 552 as did relay 560. storage group. These operate and lock up. When the operator releases the key 8, the in the same manner as the other storage recircuit through the lower windings of relays lays, relay 514 being energized in serieswith 5 560 and 561 and relay 51s is opened and relay them, on its deenergization moving the trans 61 i accordingly deenergizes, thereby opening for switch into fourth position. By the operthe circuit oi? relay 510. clay 510 is i d ation oi? relays 5'75 and 57 in the third storslightly slow to release by being provided age group, earth is connected over armature with a short circuited Winning and conse :7? to lei d 578 corresponding to the digit (5. 1i) qnently while it holds up a circuit is inoin a iniilar ma -ner the operation oi the inentarily completed from earth. arn'iature digit ke tor the remaining digits M32 7 516 and its been. contact, front contact and brings about the energization of the corre armature 512. winding of stepping magnet spending relays in the storage groups 4, 5, 5-0? to battery. Stepping inns lot 50'? there-- 6 and 7, the transfer switch being moved on 10 upon operates to advance the wipers ot the one step each time a key is released.

trani, i switch one step into engagement After the full seven digits have been sent,

with the second set of bani; contacts. however the t anster switch is moved into When the operator presses her digit hey the eighth position and upon the deer erggiza- 7 for thenezzt digit, acircuit is completed lien of relay 510 a circuit may be traced as 20 from earth, operated spring; of di -it key 7, follows: earth, armature 511 and its back conwinding of rel y 82 to battery. helay 4B2 tact eiohth contact in th hank oi wiper 538 55 e .:'l wiper. hack contact and armature upon energizin g at its armature cointint 211 pletes a circuit as follows: earth front conlead 500, wiper L70, armature 424 and its tactand armature 48:3,wiper4l56 and the con- 'l'ront contach contact in the bank of wiper 25 tact on which it is standing, working eonand said wipe. armature 485 and its tact and armature 424 wiper 470. lead 500, back ctntact, .i'irldilig of relay @86 to ha*- 90 armature 533 and its back contact, wiper 538 tery. Relay e86 is energizedin this circuit now in second position, through the lower vinding of relay 571 to lead 553 and through All at its armature 4:88 completes a circuit or stepping nmgnet 4%? so that the wipers 30 the Wilding: oit relay 5% to battery as heof the utlet finder are advanced one'step tore deserihed, The relays in all the storage and at ts armature 4L8? completes a circuit groups are provided with two windings coin for st 1%; relay 489. Tl e circuit of relay 486 nected up as shown for the first storage group is opened soon wiper 45S leaves the conand the contacts arranged s'inilarly t tact on which it was resting; and the relay is those shown for the rst storage roup ex y then dcenergized. The operation of relay iSS that the initial connection over tie arina-eur prepares tour starting circuits only one of such a. 56'? is different in each case. which however can be operative in any one A circuit is also completed by the peratil'm case since only one call can be set up at a time.

oif digit key 7 "from earth, operated. spring at in the present inshince a circuit 18 now com- 40 key 7, load 4.79, wiper and the cont-a -t p ted from earth, a i ature 4.27 and its with which it is in engag;ement vwine:v nt'eontect, front cons. t and arr ire filth M3, had 503, armature 522 and its back conon. ng oi e ay 422 1 h s; I ZW 49 2 tact-i, armature 536 and its back contz ct, wi ripen ogeratin s f. i r c-iinipletes a in position 2 tlurough the lower wind locking circuit for lofii dependently of 0t relay to lead 553 and thence to l armature dilihat arm .7 removes the tery throngh the winding of rela 51%. A ttery conncctio so as prebranch oi this circuit ext nds from back con a V other trunk 3 associated with t: ct ot armature over hack contact a Ll ih'oin enei" whei another armature hi3, back contact and a mature {all t; mature 50 through the winding oi relay 531 to hatterr. 42g

lleh J 5231 l1(:..'QVQ1 ttfSno ted ahore,isslightly 1 o g m-rmmin slow to pull up and consequently doe ni operator sent," the energize heiore its circuit in opei'led at an "trill {1 maximum f lure hi? by the operation oi relay which a I d ig (m -h at alteratii number to be ion 3311161. part (i 510 operate 2 control the stepoinn on o; J s released. l5!

l by the operation 1 the lower arri dealt- I L s 1 r 1 e wnen tne digit i ll relays 5Y1 and 5/23, battery is connected b" s nd. 486 perk. way of armature 572 to lead 5% correspond ms the same i c {By 483 ing to the digit 7. lr, however, a less number of cigits is being-V he operator will now press the Key 6, sent. all the required operations can be made he place wi iou any alteration to th whereuoon elrcuits siniilar'to those irevious- LO l i J I 1y described maybe traced over reads 502 and ao inst-as, me in miterence being that it Will now be necessary for the operator to press, the start key when she has set the digits that are required.

For the sake of convenience of description it will be assumed that the pressing of the start key orequivalent"automatic operation.

takes place before the A operator has plugged in and that the above described'effects, are produced. a supervisory circuit is completed over the lower talking conductor 303-and-the normally closed springs 348 of the emergency order wire key for relay 339. operating, at its armature 340 completes a circuit for the polarizing winding of relay 342 andalso a circuit for therelay'338'which' I latter circuit extends as follows: earth, armature 340 and its "front contact, normally closed spring 325 of the busy orcancel'key, front contact and armature 319., relay 338 to battery. Relay338uponoperating,atits armature 334 and 335 closes points in'the outgoing trunk leads, at its armature 3271 completes a locking circuit for itself, at itsarmature 332 substitutes a direct earth connection for the earth connection by way of the flashing interrupter and'its armatures328, 329,

and 331 prepares circuits for initiating flashing the generation of impulses. In this case also, only one of these ClICUltS operative at a time; The jointroperat'ion of armature and 341 completes a circuitfor.

the trunk busy lamp323- and the assignment lamp 322 so that the latter, which haspre viously been flashing under the control of the interrupter 333, will now glow steadily. I g In consequence of the operation of.arma-. ture 328, a circuit is now completed which maybe traced from earth, armature 427, and

its front contact normall closed s )11112 464 7 n.

of the sender disconnect key,1lead403, front contact and armature 321, front contact and arn'mture lea'rl'403, frontcontact and armature 321, front contact and armature 328,1ead 404, armature 436 and its front contact, winding of relay 423 to'battery. ,Relay 423 therefore ener 'izes'and upon operating,

at its armature-s 440, 441 44 and 443 cons 'nects the wipers 471,472,473-an'd 474 to the leads 407, 405, 404 and 403 respectively Furthermore at-armature 439 it removesthe battery connection from lead'f406 so that assignment lamp 332 is extinguished and "at, nrn'iature 444 opensthe circuit for relay 419. Relay 419 slowly deenergizes andat armature slowly deenergizes. v p

. The connection of earth'to lead 503 by way 429 opens the circuit for relay 418 which also of resistance 495 .completesa circuit which extends over arniature'522 and'its back contact. bac'k contact and armature 513, back contact and armature 517, windingofrelay 531 to battery. The parallel circuit extending to wiper 541 willbe Without effect if this up all y is connected to a storage relay,

When the operator plugsin,

, Relay, 339 upon can, be usefully and-hence each will be able to Wiper'is in eighth position as in the case'described. If, however, less than-the fullnumber of digits has been sent so that wiper 541 of this relay and of relay 514 in series with it is prevented by resistance 495. Relay 531 energizes; at armture 5,32 completes a circuit for relay 518, at armature 537places a holding earth on lead 504-and' at arlnature's 533, 534, 535, 536 disconnects leads 500, 501, 502,

the operation 503 from wipers 538, 539,540, 541 respectively and at the front contacts of armatures 534 and 535 connects leads 501 and 502 through to the impulsing be understood that earth is connected to lead 504at armature 537 before it is removed at armature 427; consequently all the apparatus leads 550' and 549.- Itwill i dependent on this earth is maintained oper ated. Relay 518 energizes is completed; a t armature 519 opens the circuit over lead 553 for the storage relays so as to prevent the accidental operationof any which have not yet beenenergizedfand'at' arjmature 520 opens a circuit over leads 547 and 548 for restoring the impulse sender to nor when its circuit anal in thecase of premature release. F rom'"- the earthconnection at armature 532a circuit is also completed over lead 542, back contact and armature 602, armature 608 and its I back contact, back contact and'arniature641,

armature 644 and its back contact, lead 650,

being shown in the drawings, F ig, 6), it bein field relavslwould tures 64l and 644 as "indicated by the portion shown dotted.

i or) 1.10 i understood th'at'i'f morewere prOviddtheIy: 1

would be connected up in asimilar manner v for instance back contacts of further shunt bein'cl'uded between a rma Theea'r'th potential on lead 542 also ex tends over back cont-act and armature 783 (F ig; 8-)j th'roug'rh the winding'of relay 759 and e ptertsi to battery- The interrupter 784 is arranged to control tion of in'i-pulses at the rate normally employed for operating the automatic switches, i. e. aboutlO per second. interrupter 784 closes its contacts, relay7 59 in the bridge across the iinpulsing leads 549 and 550and at armature 761; completes a em cuit for'the driving magnet 78 0of the 'im pulsecontrol switch. Upon the subsequent the genera- WVhen, therefore,

,is energized; at armature 760it opens a point wipers 615,

deenergization of relay 759, magnet? 80 is de: energized and thereupon.operates to advance the wipers 757 and 758 one step, whereupon a circuitiszcompleted by way of earthat the n'mltipled"contacts in the bank of wiper 758 and said wipertor relay 762.

elay 762 upon operating, at armature 7,6?) prepares a circuit for stepping magnet 710 of the sender control switch, at; armature 7.6 1 opens another point in thebridge across the impulsing leads, at armature 765 prepares a-circuit ior relay 860- and at armature 766 connects earth to wiper7 57 by way of back contact and armature 859. ltwill be noted that the operation of both contacts 760 and 764i is at present ineffective to send impulses over the outgoing trunk line since the impulsing leads 19 and 550 are at present bridged by armature 756 and its back contact.

In response to the subsequent energizations and deenergizations of relay 75 9,the wipers 757 and 758 are. stepped round at the rate of roughly steps per second. In the meantime, it will be remembered, the code switches are hunting to find the contacts which have been marked by the operation of the first, second and third storage relay groups as above-described. Since as previously mentioned, the code switches would preferably be ordinary rotary line switches with con tacts in the bank and as they are hunting freely they would describe a complete revolution over the whole 25 contacts in less time than it would take the impulse control switch.

" to take 10 steps under the control of the in terrupter 784. Consequently in the ordinary course when the first three digits set up by the operator correspond to an exchange code, the code switches will have foundthe marked contacts before the impulse control switch has taken 10 steps. As this is the nor,- mal. case, it will be considered first.

As may be seen from Figure 6, contacts 621, 622, and 623 accessible to the first code switch are connected up to correspond. with the code 87 6, i. e. they are connected respectively to leads 587, 57 i, 578 ghence when the 616 and 617 arrive on these contacts, a circuit is completed tor-both windings of the shunt field relay 600 which cir- Cl'lll/ extends as follows: earth, armature 582' and itsfront contact, lead armature 567 d its back contact, armature'568 and its t nt contact, armature 569 and its front. conact, lead 587, contact 621, wiper 615, right rd winding of relay 0, wiper 616, cont.... t 622, lead 574, over the contacts of the second storage relay group, armature 57 :2 to bat tery and for the other winding from earth at armature 577, contacts of the third storage relay group, lead578, contact 623, wiper 617, left hand winding of relay, 600 to battery ov erthe previously traced circuit. The shunt field relays .such' as 600and 606are so constructed that L they only operate their armaand earth to both wipers 615 and 857 upon operating, at

tures when they are energized over. both windings together by current in a certain direction. Consequently the relay 600 will only be energized when battery is connected to wiper 616 of the associated code switch 617. Thus there is no possibility of the relay 606 being energized by, a code similar to but not identical with that for which it is set, for in.- stance with two digits the same. Shunt field relay 600 upon operating, at. armature 6,02 opens ,the energizing circuit of the driving magnets thereby stopping its own associated code switch and all the others, at armatures 603, 60s and 665 connects up wipers 618, 619 and 620 and at armature 60l completesa circuit over lead 648, to]? relay 857$ Relay armature 858 connects earth over front contactarmature 765 to contact .782- in the bank or wiper 757. and at armature 859 connects wiper 757 to the winding. of relay 767 instead of to earth. Consequently when the wiper 757 engages with the contact 7 82,-which will happen very shortly after the energization of relay-857, a circuit is completed from earth, front contact and armature 858,,1' ront contact. and armature 765, bank contact 782, wiper 757 ar-' mature 859 and its front contact, winding oirelay 767 to battery. .fRelay 767 upon operating, at armature 769 completes a locking circuit for itself dependent uponarmature 766, at armature. 770 completes a circuit for effecting the automatic rotation of the wipers of the impulse control switch to their home position, at armature 783 opens the circuit of impulsing relay 759 and at arms..- ture 768 completes a circuit for relay 751. The circuit ofrotary magnet 780 extends from battery, winding of magnet 780, interrupter contact 781, *lfront contact and armature 7 70, wiper 758 to earth at the multipled contacts in. the bank; wipers 757 and 758 are thus rotated until wiper 758 engages contact 7 85, which is left dead. 'When this occurs the circuit for relay 7 62 is opened and it deenergizes after a short interval owing.

to its slow to release characteristic, When armature 766 leaves its front contact, the locking circuit for relay 767 is opened and it also commences to deenergize .slowlv. When relay 767v has completely deenergizei the circuit for impulsing relay 759 is again completed and a freshrotation of the impulse switch commences.

' Relay 7 51 is energized vhen-its circuit is completed at armature 768 and at its arma-' ture 7 5 completes a locking circuit for itself to the earth on lead 542, at armature 7 52 places earth on wiper 700 of the sender control switch at armature 7 53connectslead 650 to. the lead 788 which servesno useful purpose in the present instance,.at armature 755 prepares a circuit over lead 787 for magnet 716 and at armature 756 removes one of the shunts around armature 760 so that this armature may now be effective in sendinn; impulses out to the distant automatic switches. Owing to the operation of armat-ure 7 52, a circuit may be traced from earth at back contact and armature 752, lead 7 86, wiper 7 and the first contact in its bank, lead 704, armature 863 and its back contact, lead 651, armature 611 and its bank contact, armature 605 and its frontcontact, wiper 620, contact 626, lead 632 to terminal 711 on the left hand side of the intermediate distributing frame, hereafter referred to as thelllE' f .7 I

Suppose in the present instance that. the code 876 set up by the operator is to be converted into 395 for operating tl'ieappro priate switches: In that case terminal 711 will be cross connected to terminal 703 on the right hand side of the I. D. F. so that earth wi l be extended over lead 743. to the terminal 7 87 corresponding to the digit 3 in the bank of wiper 757.

In connection with the operation of the impulse control switch, it should be pointed out that on the first opening of contact 760 after the switch leaves itsnormal position this contact is shunted by contact 764 since the relay has not yet operated, but that further operationsof contact 760 result in the production of interruptions of the trunk circuit since the parallel'contacts 76tand 765' are now both open. The circuit across the outgoing trunk may be traced as follows: from the upper talking conductor 336-over the normally closed springs controlled by .relays 315, 314i and 313, front contact and armature 316, lead 405, front contact and armature 441, wiper 472, lead 502, armature 535 audits front contact, lead54-l9, armatur 760 andvits back contact, lead 550, front contact and armature v53A,]Fead 501, wiper 471, :un'iature 440 and its front'contact, lead 407,- armature 317 and its front contact, normally closed springs controlledvby relays313, 3 14 and 315 to the-lower talking conductor 337.

Upon the de-energization of rela-y'767, the

V in'ipulsing relay 759. will. again operatev to step the wipers 757 and 758 round and;

410 open contact 760 until three fimp'ulseshave been sent out, whereupon Wiper 75.7 will on gagewith contact 787. A circuit will then he completed from armature 752 as previously traced over wiper 757, armature 859 and its front contact, Winding of relay 767 to battery. delay 767 therefore operates with the results previously, described, namely, that the, circuit of the impulsing relay 759 is opened and the impulsecontrol switch is automatically returned to its normal position, whereupon relays 762 and 767 deenergize.

It will be observed that assoon as relay'7 62.

energized the secondtime a circuit was completed from-earth over wiper 758, armature 763 and its front contact, armature 755 and its front contact and lead 787 for the driving magnet 710 of the sender control switch. This magnet thus remains energized as long as the wiper 758 continues to find earth but as soon as it reaches the dead contact 7 85 or the corresponding contact in the other half of the bank, the magnet 710 will be deen'ergized and will operate toadvance the wipers700, .701, 702 and 703 one step into engagement withthe next set of bank contacts. The earth from armature 752 now extendsover lead 786, wiper 700, lead 705, armature 862 and its back contact, lead 652, armature 610 and its back'contact, armature 604 and its front contact, wiper 619, contact 625, lead 631 to terminal 712 on the left hand side of the Ll). F.- According to the assumption made above, this terminal-is cross connected to terninal v799 on the right hand side of the l. D. 16 consequently, the earth is extended over-lead 74-9 to the contact corresponding to the digit 9 in the bank of Wiper 757. It should be mentioned that the second half of the hanlis'of wipers 757 and 758 is connected up'in the same way as the first half, so that the switch has two normal positions from .either of which the'operatioii is the same. Upon the, deenergization of both relays 762 and 767 relay 759will be again energized and will, operate intermittently to control the stepping'of the wipers'757 and 7 58 over their -transmission' overthe outgoing trunk line. In this case it Will be seen that nine impulses will be sent out before relay 767 is again operated and the generation of impulses, stopped. I

When relay 7 62-deenergizes the circuit for magnet 710 is again opened and upon-deenergizing it operates to step the vvipers' of ;nected to terminal 735 on the right hand side consequently the earth connection extends over lead 7 -150 the contact corresponding to the digit 5 in the bank of Wiper 757. In this ,case, therefore five impulses will be sent out over the outgoing trunk line, after, which relay7 67 will be energized and will operate respective banks and to generate impulses for contact, wiper 618,

7 the sender control switch into their third to stop the sending of further impulses and I to effect the automatic rotationof the Wipers of the impulse control switch on to their nor-' mal position. 1

sequent .openingof contact 7 63', magnet7l0 is deenergized and the sender control switch Upon the release .of 615137762 and the conis moved a further step. A circuit is now completed from earth, armature 722 and its back contact, hack contact and armature 728, fourth contact in the bank of Wiper 702 and said Wiper to magnet 710 by Way of its interrupte cont-act; consequently the Wipers 'ZOO, 701, 702 and 703 are moved a further step. In the iii th position of the wipers a circuit is again completed over armature 721 and 752'? so that the switch moves into sixth position. In this position also magnet 710 is energized from earth at mature 720 over wiper 702 consequently the wipers are HIOVGCl into the seventh position. lhereupon Wiper 7G2 encounters a permanentearth connection that the sender control switch is moved into its eighth position. I

in this position the earth il ron'l armature 752 extends over wiper 700 in eighth p and lead 583 to the iii-st contact ot the fourth storage relay group and thence over the appropriate operated center is to loan. which is connected to leadllfi and thus to the hau of wiper 757. Hence by the operation of relays 759., 762 andTtE? in the inalrier previsen t ously described, live iuipulsa'rs w ll be over the outgoing trunk line. Upon t energization oi control switch reachesits normal posr ion, the sender control switch is moved on one step in p'repa ation iior the sending; of the 'acoud numerical dig in this case earth will he connected to lead 580 and henceto lead M l and tour impulses will be sent out. in a similar manner two further trains consisting of three and two huge ses will he sent out.

The sender control switch is thus stepped on iito its twelfth position in which earth is connected over wiper T00 and lead 790 direct to lead 588, in consequence of which a further train compri. 'ng a. single impulse is sent out, this train being; additional to the i'iuinher up by the operator on the keys. 'lhis. additioual in'ipulse is to indicate in case the call is 'oiny; to an ope 'ator at a call iinlicator position, that the call in question has come from a u'icchanical tandem exchange and not direct i'lOlIl an automatic sahscribor. case the all were going direct to an automatic suhscriber, this extra ii'upulsc would have no deleterious ei'icetbut would simply be ahsorbed. It will be uiulerstood however that this all indict tor impulse is by no n'ieaus essential, to the proper w rhing of the system and that in many cases it may be desirable to omit it altogether.

Upon the termination or this extra L 1.! dicato iinoulse, the wipers ot the sendcrcontrol switch will he moved into the thirteent posit-ion, whereupon the. followup; circuit is completed: earth, wiper 703, lead 5 H", upper Winding of relay 52l to battery. Relay 521 thereupon operates atarrnatur i 523 opens t; circuit of relay 531 and at a mature 523 reay 762 when the impulse switcl: through relay {ft is preventml.

gained no 1,705,1eee

moves earth at the front contact 537 from lead -:l anl hen from ead 4-03.

in consequence of which the sende' guard 1 lainp are is extinguished "nd relay 422 and :1 rela 312 deene'r iz Upon thee riseucrt h opening 0 a: contact @106, earth relav released. Relay BQ'l als closes an er point in the lead 506 ror moving on the outlet case all the senders in the group are busy ope 'ation becoming e'tlectiic after the o inn; 0t contact 530. v

Upon the dcencraization oi relay 551, rela 5539 is released by the remoral or e if 1 .i'nature 537, asare also'all the opera ed sere. clays which were locked up tov leat lurtherinore at contact 532 the circi 1 rel-a y 518 is opened and earth is removedi leads 50 1- and 542.

apparr Lu l; 1 chain c "reui Y In consequence of therei'uoyal of earth from lead 55 l'and of there-- l ase oi? the storage relays, the shunt t'eh relay which has ceen operated. is deenergiz id and in consequence ot the removal of earth from lead 5&2, the relay 751 is released and the further operation oi" the impulse control lay is deem-spiced when its circuit is opened at contact 601 on the release of the shunt field relay GOO.

Upon the deenergization of relay 525i, (-5. armature 526 earth is again connected to lead an to prevent the sender being seized again before it has completely restored to norinal and a circuit is also completed for release magnet 508 of the transfer switch by ay of the oil norinal contact 509, so that this switch is returned to normal. At armature 5:2? earth is connected to lead 54-3 and thence to the Hull tipled contacts in the hanlr ot wiper 701, so

-t ut the sender control. switch is automatically restored to its normal position. j As long as the sender control switch is in an oil norposi ion. this-earth ext-ends over lead S ll 1nd armature 5325i and hack contact to'the z 521 and will maintain V l so to prevent the sender being tahe w before'it has re- "na po 'lhe engage- .nentor armature 529 with its back contact serves no useful purpose in the present instance since the wiper 758 to which it is connected is moved to its normal position belore the releasing operation commences. The arnature 530 opens a point in the'chain circuit for busying the group of senders but as this u relay e armature has been shur ed by armature see as previously- :described this operation is also without effect. I

i l hen wiper *ZOl. reaches its 1101111211 position, release relay 5-21 will receive no more current and willconsequently,deenergize.

7 All the operated ,apparatus-hasthen been released and thev sender maybe taken into'use for the setting up of a new connection.

v In the trunk circuit the deejnergization of relay 312 completed thespeaking leads and the wanted party .would be notified in. the usual manner. When he replies thedirection of current flow is reversedover the speaking leads in consequence ofw-hich polarized relay 342 is now able to operate and at its armature 343 it then connects the retardation coil 345 to lead 302 so as to give the Aoperator answering supervision. Relays 338-and 339 remain energized for the remainder of the. connection until the A operator removes her plug- When this occurs, relay 339 is deenergized; at armature 340 it opens the. circuit of relay 338 and at armature 341 extinguishes the trunkbusy lamp323, thus indicating to the B operator that the junction line is, idle and maybe used for another call. p i

Consider now the case in which owing to some mistake on the part of the. operator,

she has setup a number the first three digits of which do not correspond to any exchange code, in which case, unless special provision were made, the code switches would continue hunting without result.

According to the arrangement shown, however, if no shunt field relay is operated bythe time wiper 757 comes into engagement with ,contact 782, the following circuit is completed; earth, armature 7 65, and its front contact, back contact and armature 858, normally closed springs controlled byarmature 8 6 4, winding of relay 860 to battery. Relay 860 accordingly operates, at its armature 864' looks itself up to lead 542, at armature 865 completes a circuit for relay 857 and atarmatures 861, 862 and 863 transfers the leads 706, 705 and 7 04--from the first three contacts in the bank of wiper 700 to leads 801, 802 and B03 respectively which leads are connected to terminals 806, 805. and 804 on the left hand sideof the 1.1). F. Relay 857'operates quick-' ly when its circuit is completed anda circuit} may then be traced from earth at the front-- contact of armature 858 and said armature,

front contact and armature 765, bank con tact 782, wiper 757, armature 859 and its front contact, winding of relay 767 to battery. Relay 76.7 accordinglyoperates, at its armature .783 opens the circuit of the impulsing relay 7 59, at armature 770 completes a circuit for restoring the impulse control switch to its normal position, at armature769 completes a,

locking circuit for itself and at armature 7 68 priate. contacts on theright hand side of the I. D. so as tos'end the requisitecode, In

case-lessthanthree digits should be required to reach. the dead number operators position,

suitable cross connections will bemade to the first three contactsv in the bank of wiper 702 of the sender control switch. For. instance,

suppose thatonly two digits are required; I in that caseterminals 804. and 8.05 .will be cross connected respectivelyto the. terminals on theright hand side. of the I. D. corre spondingto these two digits, while terminal 806 will be. connected to contact 809. Underthese circumstances when the sender control switch is moved to its third position after the two digits have. been sent, Wiper 702 will find earth overcontact 809 and wiper 7 00 andthe switch'will-be immediately moved into fourth positionand on into eighthposition as previously described; If only one digit is required for reaching the operators position, terminal 805 will be cross connected to con met 808 inwhich case thesender control switolrwilln ove on automatically from posit on 2 to position8. For a call of this nature,

it isclearly not necessary for anynumerical d gits ,to' be sent and the impulse sender may be releasedas soon. as; sufficient digits have been sentto reach an o'peraton Th s is taken careg'ofover lead 788 since when'the sender control switch arrives inpos tion 8 a circuit maybe tracedas followsz'earth, armature 5 32- and its front contact, lead 542, back contact and armature 602, armature 6.08 and its back contact, back contact-and'armature. 641, Parinatulje 644and itsback' contact, lead 650,

armature 753 and its front contact, lead 788, I

eighth oontactinthe bankfof wiper 7 O3 and saidwiper, lead 546, upper'winding of relay 521 to battery. Relay .521 is thus. operated and initiates the release of all the operated apparatus in the manner previously de- :iscribed. a i

For calling an operator direct, for-example for toll calls or information, thesingle digit 0 is s ent, in which case it will clearly be necessary for the B operator to press the start key before the sending ofimpulse will commence. When earthis connected to lead 554 as a consequence of the operation of relay 531, this earth is extended over the operated armatures of relays 565 and 566 to the 0 digit relay 6.06.

This thereupon operates, at armature 608 r opens the starting, circuit for the code switches'so as to prevent useless hunting, at armature 607 completes a circuit forrelay 857, and at armatures 609, 610, 611, connects the first three contacts in the bank of; wiper From these suitable; cross connections are made to the right liandside to control the .700 byway ofleads 612, 618,614 to special ,termin'als on the left hand side 0f the I. D. F.

generation of the trainsof impulses necessary to, routethe call to aniopera'tor. Clearly n t s a e. als rrangemen smay rea i ybe made for sending only one or two digits and only comparatively simple additional connections would be required if it should be necessary to send four or five digits. This will be more readily understood from the description of the various special code relays which will now be given.

It may happen in exceptional cases that it will be desirable'to send either more or less than the three digits for an exchange code which are provided for in normal Working or that the, special code is such that no numerical digits are required. From what has been said already in connection with dead number calls, it will. be clear that if less digits are required a proper operation of the various switches may be effected by cross connections from the I. D. F. termmals connected to the contacts of the code line switches to the requisite contact or contacts in the bank of wiper digits are to be sent: This case is taken care ofrby relay 723. Suppose that the first code switch finds the marked contacts and comes to rest on contact 629 and its associated contacts. WVhen the start key is pressed or the corresponding automatic operation has taken place, the following circuit will be completed earth, front contact and armature 752, lead 786, wiper 700 and the first contact in its bank, lead 7 O4, armature 863 and its back contact, lead 651, armature 611 and its back contact, armature 605 and its front contact, wiper 62(), contact 629, lead 635, normally closed springs controlled by armature 726, winding of relay 723 to battery. Relay 723 operates, at armature 726 locks itself up to the earth on lead 542, at armatures 72 1, 725 and 729 prepares circuits to terminals 810, 811 and 812 on the left hand side of the I. D.

F., and at armatures 728 and 727 removes earth from the fourth and fifth contacts in the bank of wiper 702.

It will now be seen that the first digit sent out will be in'accordance with the terminal on the right hand side of the I. D. F. which is cross connected to terminal 812. The second and third digits are determined by connections from the contactsengaged by wipers 619 and 618 which lead to terminals on the left hand side of the I. D. F. from which the required cross connections are made. The fourth digit will be determined by the cross connection from terminal 810 while the fifth digits will similarly be determined by the cross connection from terminal 811. After the five digits of the converted exchange code have been sent out, the numerical digits will be transmitted in the manner previously described and the subsequent'releasing operation is as before.

In case the three digits of the exchange code set up by the operator are to be converted into six digits the general arrangements are similar. In this case it is assumed that the first code line switch comes to rest on contact 628 and its associated contacts, whereupon, when the start key is pressed, a circuit is completed for relay 71 1. This relay'energizes,

locks itself up at armature 719 and at armatures 715, 716, 717 and 718 prepares'circuits for suitable cross connections'in a manner similar to that described for relay 7 28. The only difference is that an extra armature is provided to connect up the terminal which controls the sixth digit and that earth is re moved at armature/720 from the sixth contact in the bank of wiper 702 so as to prevent the switch running through this posit-ion. The remaining operations ta ke place in a manner which will be readily followed from what has gone before. I r

The functions and method of operation of relay 730 will now be described. This relay will be energized when contact 532 closes if the first code switch has come to rest oncontact 627 and its associated contacts. Relay 730 upon operating, at armature 732 looks itself up to lead 5 12 and at armature 73]. connects earth to terminal 813 on the left hand side of the I. D. F. This terminal is con nected according to requirements to one of the contacts in the bank of wiper 7 03 and permits switching through and the release of the impulse sender after any desired number of digits have been sent. For instance if terminal 813 is cross connected to terminal 814 relay 821 will be energized and the impulse sender released after five digits have been transmitted.

It should be noted also that bysuitable cross connections from the left hand side of the I. D. F. to the switching terminal 815, it is possible to switch through as soon as the exchange code has been transmitted. or after one or more numerical digits have been sent. If such a connection is made however it is necessary to sacrifice one terminal which could be used for controlling the generation of a train of impulses, so that in some cases it will be more desirable to effect the same result through relay 730 which can be common to several codes.

In case the operator makes'a mistake in setting up the wanted number and discovers it before the'complete number has been set up, that is, before the operations corresponding to the pressing of the start key have taken place, she is enabled to cancel thedigits already set up by pressing the cancel key 184:. This brings about the operation of relay 448 which at its armature 450 completes a circuit for relaye l'f. At its armature 1 removes earth from the holding lead 1, and at its armature 156 removes earth from wiper 4255 so as to prevent another operator from seizing this set of impulse sending equipment during the momentary removal of earth from test wiper 1-7 1. Relay e7 7 energizes when its circuit is completed and at armature 449 I opens the circuit of relay 448 and connects t.-. self up in dependence on the key 484. Relay 448 being slow to release remainsoperatcd for a short while which is the same'however long the key is pressed. The removal of earth from lead 504 releases all the Operated storage relays and also relay 525 which by closing its contact 526 effects the return of the transfer switch to normal. may now'proceed to set up the right number and in this case will use'the sameoutlet and impulse sender.

In case the sending of impulseshas actually.

commenced before the operatordiscovers her mistake, she will press the-busy-or cancelkey associated with the trunk line which has been taken. into use, the effect of this being to open the locking circuit for the relays 338 and 312. Upon the 'deenergization of these relays the circuit of relay 531 is openedat armatures 321 and 328 so that this relay deenergizes and releases all the operated apparatus in the set of impulse sending equipment in'the manner previously described. The operator will then press the assignment, key 304 again whereupon another impulse sender set will be seized over another outlet, (since the outlet finder was stepped on when impulse sending commenced) and the connection maybe completed-in the ordinary way. If theimpulse control-switch should be in an off normal p0 in order to enable the inter-exchange junction,

line to be used as an order Wire in case of necessity. When this key'is operated, the connections of conductors'302 and 303 to the trunk circuit relays are broken at springs 346 and 348'and these conductors are connected at springs 347 and 349 to the leads 351 and 352 which can beextended to the operators head. set. Atspring 350 a circuit is'completed for the trunk busy lamp 323 which is thus lighted to indicate to the operator that the trunk line cannot be used for outgoing connections.

Should a junction line be out of order and therefore not available for use, the operator will press the busy key associated with that line. In this case the only effective operation will be the completion of the circuit for the busy lamp 323 at springs350, so that the operator is notified that the line must not be used. Inspection of Fig. 2 will show, however, that should the operator assign the line in error it will be impossible for an impulse sender to be associated with it permanently The operatorcircuit and. the lamp 322'willnot light in the ordinary manner.

.Incase one of the outlets should be. out of order, it will be necessary to operate the associated sender disconnectkey. 'At the left hand-- spring of this-key the energizing circuit for relay 420 isopened at spring 462 and at spring 461 earth is connected to the corresponding contact in the outlet finder. so as to prevent this particular outlet being taken into use. At the right hand spring of. the

key a circuitis completed for the sender guard lamp 476 at the spring 463 and at 7 spring 464 the energizing circuit forthe relay 312 is opened.

The case when all the-sendersaccessible to asender selector are busy is taken care of by a chain circuit extending over contacts 524 and 530 in parallel and over similar contacts on other impulse senders in the group to,

earth. lVhen all the impulse senders of a group are in use therefore, a c1rcu1t is completed for relay 421, which uponv operatingyat armature 435 connects earth to armature 466,-

at armature 434 opens the energizing circuit of relay420 and at the front contact of this armature connects earth to the contact corresponding to this outlet in the bank of the outlet finder. One effect of the connection of earth to the contactwith which Wiper 460 is in engagement is to complete a circuit for relays 410 and 409 in series. Relay 4l0energizes and at its armature 466 opens a point in a circuit for the drlvingmagnet 467 and relay 409 also energizes a short while after and at armature 465 closes another point 1n this circuit which consequentlyv doesnotbecOme operative. Theearth connection through relay 410, whlch 1s of very low. resistance, also extends over lead 400, armature 311 and ts other assignment'relays, armature 310 and its resting contact lead 401, interrupter contact 468. to driving magnet 467. Driving magnet 467 accordingly operates and advances the switch wipers one step into engagement with the next setof'contacts. In case all the senders accessible by way of. this outlet also are busy,;there will be earthon the contact with which wiper 460 is now in en gagement and the switch. willv continue to hunt until an idle outlet is found over which the connection can becomplete It might happen in some cases'that the outlet which has only ciated sender selector is hunting for this sendbeen preselected has access to. one dle sender and that whilethe asso resting contact, chain of similar contacts on or it is'taken into use fI'OihSOlllB other operators position. v It is clear that unless special provision were made the sender became free and unnecessary waste of time and wear of the switch would be occasioned. In this case also therefore it is necessary for the outlet finder to step on tofind a new outlet but the traced above is no longer; operative armature 4:66 completes acircuit from earth,

front contact and arn'iature L of relay el'll,

armature 466 and its back contact, armature l6?) and its trontcontact. interrupter contact 4l68 to driving n'iagnet let. The outlet iinder is thus automatically stepped on to find a free outlet and unnecessary hunting of the sender selector and waste of the ope ators time are avoided.

It may be desirable at this point to exp ain the precise nature and operation of the lamp signals which are provided to indicate to the operator the progress ot'tlie connection. As has already been explained, the opera or holds the assignment key pressed until the assignment lamp 322 lights. ll the A o erator has not already plugged in, the lamp 322 will glow intermittently under the control of the flashing; interrupter 333, and will continue to flash until their operator does plug in, after wnich it will glow steadily until the sending of impulses commences. At the time the sender guard lamp lZS will light and glow steadily to indicate that an outlet in use. As has been pointed out, it the A operator is a trifle late in plug ing in, this operation will control the starting oi the sending; of impulses and consequently i this case the lamp 322 will continue to flash until it is e;i-:- tinnuished.

The trunk busy lamp 328 will always he lighted when the A operator plugs in; in case the B operator should not have pressed her assignment hey, the lan'ip will ii h until the key is pressed and an lie impulse sender is found, whereupon it will glow continue to do so until the connection is taken down. By means oil these lamp signals the l) operator is kept fully informed at the progress of the connection except that she is not given answering: supervision when the calling suhserilicr replies as this is clearly unnecessary. The sender guard lair remain lighted as long; as the particular outlet" is in use or the sender disconnect hey is operated.

A description may now he given oithe apparatus shown in the lower part in. I purpose of which is to obviate the possibility of two operators seizing the same impulse i-is sender at the same time. The relay such as lOS are individual to each operators position and each 1s connected to the leaol corresponding to lead lO-O so that it will energize when 4:09 and 410 are energized and substitutes an steadily and assignment key in'the position is I Relay 4:08 controls two armatures and 453 in chain circuits which include contacts controlled by the relays similar to .08 associated will all the other posi ions havaccess to the same group of impulse senders. The former of these circuits comprises a closed series chain ci cuit extending; throiiigh the armatures and back contacts. while the arn'iatures are also connected to appropriate contacts in the haul; of wiper The front contacts at these armatures extend to arinaturcs such as 432 and are thus inclu led the energizing circuits of the cutoil relays such as (19. It will he remembered ll?) was traced from ever any pressed.

tnat the circuitfor relay earth at resting contact and armature 49%, chain of similar contacts on other cancelling relays, armature 456 and its resting contact, wiper and the contact with which it is in engagement, armature 452 and its working contact to relay 419. It will he seen that it only one relay such as s08 is operated at a time and thewiper s in a different position from that shown, a ircuit for'relay 419 will still be oomle 'ted over the armatures such as 452 and haclr contacts. When, however, there isniore than one relay d08 operated at a time, in which case wiper 455 will he rotating, as ahoutto he explained, cirpleted in turn as wiper 455 comes into engagement with the contact connectedto the arm-a ti centrolled by the particular relay. By this means it isinade certain that no two operators can possibly seize the same impulse sender owi to their respective sender selectors coming to rest at the same instant on multipled contacts. In. order to that the wiper lfif) shall rotate when at least two operators press their assignment keys simultaneouslyghut nototherwise, the second cuain circult including contacts e253, 4193 and @9 1 is n'iade use oil. It will be apparent from inspecti on oil the drawing that as long none or on v one of the relays 4:08 is operated, a cirt ."l for the driving h t as soon as on ators, only one may impressing; an asient key at an particular instant. The

earth connection to the wiper 455 is taken through additional contacts on the cancellatlon relay such as a l?) in order that it an operator presses hcr cancel key 48% where upon earth is momentarily removed from the multiple test contact in the hank out wiper ice 

